A critical issue in integration of porous materials, such as e.g. low-k materials, in semiconductor processing is the degradation of their properties, e.g. their dielectric properties as expressed by its dielectric constant k. Porous low-k materials are more sensitive in comparison to conventional dielectric materials such as, for example, silicon dioxide. The open porosity of porous low-k materials significantly increases diffusivity of water species. As a result, polar water groups are incorporated into the porous structure which may increase the dielectric constant or k-value of the material. This leads to an increase in k-value for the porous material and converts the inherently hydrophobic low-k material into a hydrophilic material. Subsequent adsorption of moisture, e.g. water, or other polar molecules having high polarizability, mediated by hydrogen bonding, can significantly increase the effective k-value of the material, e.g. to a k-value>>80.
To avoid water absorption and/or water radicals into the pores of the low-k material during patterning of the low-k material in a dry etching chamber it has become increasingly important that the environment inside the processing chamber is clean and that water residues are avoided. As is known in the art, many of the processes carried out within the semiconductor processing chambers leave deposits on the inner surfaces of the processing chamber.
The currently used chamber walls cleaning recipes in low temperature operating chambers (20° C.-75° C.) are introducing water on chamber walls (as a by product reaction of cleaning chemistry with polymers on chamber walls). The water bonded on the chamber walls is released during the plasma processing. The released water is a source of additional O* and H* radicals in the used plasma mixture as shown in FIG. 1. The presence of the additional species released from the chamber walls (such as H* and O* radicals) during the process has an influence on the plasma processing of the material. Moreover after the conventional cleaning some amount of particles bonded to the plasma chamber walls still remains.
The typical plasma cleaning chemistries use SF6 and O2 based chemistry. The SF6 plasma removes polymers on chamber walls and O2 removes residual carbon but these plasma cleaning chemistries do not remove water residues.